Integrated optical latch

ABSTRACT

Techniques are disclosed for optical switching and data control, without the interaction of electronic switching speeds. In one example embodiment, a common cavity optical latch is provided that that can hold an optical state for an extended period of time, and the operation of which is controlled optically. Optical phase control allows optical modal switching to be employed between two common optical cavities, using incident optical signals and the way in which the cavities manipulate the phase within them to lock in one or the other configuration, thereby forming an optical latch. The optical latch is implemented in an integrated fashion, such as in a CMOS environment.

RELATED APPLICATIONS

This application is related to U.S. application Ser. No. ______(Attorney Docket 20070094), filed Aug. 29, 2008, and titled “SalicideStructures for Heat-Influenced Semiconductor Applications” which isherein incorporated by reference in its entirety. This application isalso related to U.S. application Ser. No. ______ (Attorney Docket20070095), filed Aug. 29, 2008, and titled “Two-Step HardmaskFabrication Methodology for Silicon Waveguides” which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to optical communications, and more particularly,to an optical latch.

BACKGROUND OF THE INVENTION

Digital electronics such as logic gates are commonly used inimplementing circuits of all kinds. In some such applications, however,the speed at which the gates can switch is limited, by both the gatesthemselves as well as the clocking signals that enable the switching.Although optical circuits can be used to improve speed, there areoftentimes still instances where optical circuitry interfaces withelectronic circuitry, giving rise to switching delays. Moreover,conversion circuitry is needed at the optical-electronic interface, sothat optical signals can be converted to electronic signals, andvice-versa. This conversion adds complexity and cost, in addition todelays associated with the conversion process itself as well as withswitching delays.

There is an increasing need, therefore, for optical switching and datacontrol.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an integrated opticalcircuit device. The device includes a first integrated waveguide loopfor guiding optical signals, a nonlinear phase shifting element forphase shifting signals in the first waveguide loop, a tunable couplerfor providing an input pulse in both clockwise and counter-clockwisedirection of the first waveguide loop, and an input coupler forproviding a control pulse in at least one direction of the firstwaveguide loop. The first waveguide loop can be, for example, a highindex contrast (HIC) silicon waveguide. The nonlinear phase shiftingelement may include, for example, n individually tunable resonantelements. In one such case, the nonlinear phase shifting elementincludes a salicide heater structure for providing heat to the nindividually tunable resonant elements. The nonlinear phase shiftingelement may include one or more tunable couplers configured withsalicide heating elements for optically coupling resonant elements tothe first waveguide loop. Such heaters can be used to change theeffective phase delay and coupling coefficient associated with suchoptical elements. In one specific embodiment, the first waveguide loopis configured with an inner ring and an outer ring optically coupled tothe inner ring, and the nonlinear phase shifting element is in the innerring. The device may includes a second integrated waveguide loop forguiding optical signals, a nonlinear phase shifting element for phaseshifting signals in the second waveguide loop, a tunable coupler forproviding an input pulse in both clockwise and counter-clockwisedirection of the second waveguide loop, and an input coupler forproviding a control pulse in at least one direction of the secondwaveguide loop. The second waveguide can be, for example, a high indexcontrast (HIC) silicon waveguide. The nonlinear phase shifting elementfor phase shifting signals in the second waveguide loop may include, forexample, n individually tunable resonant elements. In one such case, thenonlinear phase shifting element for phase shifting signals in thesecond waveguide loop includes a salicide heater structure for providingheat to the n individually tunable resonant elements. The nonlinearphase shifting element for phase shifting signals in the secondwaveguide loop may include one or more tunable couplers configured withsalicide heating elements for optically coupling resonant elements tothe second waveguide loop. In another specific embodiment, the secondwaveguide loop is configured with an inner ring and an outer ringoptically coupled to the inner ring, and nonlinear phase shiftingelement for phase shifting signals in the second waveguide loop is inthe inner ring.

Another embodiment of the present invention provides an integratedoptical circuit device. The device includes a first a nonlinearinterferometer optical comparator that includes a first integratedwaveguide loop for guiding optical signals, a nonlinear phase shiftingelement for phase shifting signals in the first waveguide loop, atunable coupler for providing an input pulse in both clockwise andcounter-clockwise direction of the first waveguide loop, an inputcoupler for providing a control pulse in at least one direction of thefirst waveguide loop. The device further includes a second a nonlinearinterferometer optical comparator operatively coupled to the firstnonlinear interferometer optical comparator that includes a secondintegrated waveguide loop for guiding optical signals, a nonlinear phaseshifting element for phase shifting signals in the second waveguideloop, a tunable coupler for providing an input pulse in both clockwiseand counter-clockwise direction of the second waveguide loop, and aninput coupler for providing a control pulse in at least one direction ofthe second waveguide loop. Each of the first and second waveguide loopscan be, for example, a high index contrast (HIC) silicon waveguide. Eachof the nonlinear phase shifting elements may include, for example, nindividually tunable resonant elements. In one specific embodiment, eachof the nonlinear phase shifting elements includes one or more salicideheater structures. In another specific embodiment, each of the first andsecond waveguide loops is configured with an inner ring and an outerring optically coupled to the inner ring, and each of the nonlinearphase shifting elements is in the inner ring.

The features and advantages described herein are not all-inclusive and,in particular, many additional features and advantages will be apparentto one of ordinary skill in the art in view of the drawings,specification, and claims. Moreover, it should be noted that thelanguage used in the specification has been principally selected forreadability and instructional purposes, and not to limit the scope ofthe inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a nonlinear interferometer optical comparatorconfigured in accordance with an embodiment of the present invention.

FIG. 2 illustrates a nonlinear phase shifter configured in accordancewith an embodiment of the present invention.

FIG. 3 illustrates an optical latch employing external optical sourcesCW1 and CW2, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Techniques are disclosed for optical switching and data control withoutthe interaction of electronic switching speeds.

In one example embodiment, a common cavity optical latch is providedthat takes advantage of the fact that dense integration of low losswaveguides in silicon can be achieved in a way that allows precisecontrol of phase. This control of the optical phase allows optical modalswitching to be employed between two common optical cavities, usingincident optical signals and the way in which the cavities manipulatethe phase within them to lock in one or the other configuration, therebyforming an optical latch.

The optical latch is implemented in an integrated fashion, such as in aCMOS environment on a silicon substrate. Such an optical latch can beused, for example, in almost any application where a data bus isrequired. Numerous applications will be apparent, such as in opticalcomputers and data transmission systems, or other such systems where itis desirable to eliminate or otherwise reduce the influence of slowerelectronic circuits and the complexity associated therewith, and incases where it is desirable to hold an optical state for an extendedperiod of time.

Nonlinear Interferometer Optical Comparator

FIG. 1 illustrates a nonlinear interferometer optical comparatorconfigured in accordance with an embodiment of the present invention. Ascan be seen, the optical comparator includes an integrated waveguideconfigured with a tunable coupler, a nonlinear phase shifter, and aninput coupler.

The tunable coupler has a coupling factor that can be adjusted or‘tuned’, by operation of lateral salicide heaters included in thetunable coupler. In operation, when an input signal or pulse is provided(e.g., via CW source), the pulse is received at the tunable coupler anda portion (determined by the coupling factor, k) of the pulse follows aclockwise path around the waveguide, and the remainder follows acounter-clockwise path around the waveguide. The coupling factor can beset in accordance with the thermo-optic effect, by applying heat to thetunable coupler using the lateral salicide heaters, which provide theheat when power or a suitable bias is applied to the heaters. Thesalicide heaters will be discussed in more detail with reference to FIG.2, and additional details are provided in the previously incorporatedU.S. application Ser. No. ______ (Attorney Docket 20070094)). In anycase, because of phase shifts across the tunable coupler both into andout of the waveguide loop, these pulses interfere and normally cancel onthe output and add at the input.

Thus, the net effect is reflection of the input pulse from the opticalcomparator. This cancellation is assured in a Sagnac interferometer asthe pulses transit identical paths and thus obtain equal phase shifts.By making the tunable coupler unbalanced, such as 70:30 instead of50:50, the pulses in each direction have unequal intensities. Thenonlinear phase shifter element then produces unequal phase shifts dueto the unequal intensities. They then do not destructively interfere atthe output, and the input pulse effectively switches, or couples, to theoutput path. This intensity-dependent optical switching (or comparison)is based upon Self Phase Modulation (SPM). Should a different pulseenter the control arm (via the input coupler), the nonlinear phase shiftis caused by Cross Phase Modulation (XPM).

Because a threshold control pulse enters the loop in just one direction(by operation of the input coupler), it allows the tunable coupler to bereturned to 50:50 coupling, and the waveguide loop will switch between 0and 100% of the input when the sum of the input pulse plus an intensitycontrol pulse exceeds the loop threshold (differential phase shift ofπ). This provides a settable/changeable threshold for the opticalcomparator. The output pulse manifests when the input pulse exceeds thecomparator threshold (quantizer level wavelength encoding).

The waveguide, as well as the tunable coupler, input coupler, andnonlinear phase shifter, can be implemented, for example, in silicon,such as a wafer or silicon-on-insulator (SOI) platform. In someembodiments, conventional integrated waveguide fabrication techniquescan be used. Alternatively, and in other example embodiments, thewaveguide can be fabricated using a two-step hardmask methodology asdescribed in the previously incorporated U.S. application Ser. No.______ (Attorney Docket 20070095), as will now be described.

In general, the two-step hardmask fabrication process can be used toform a waveguide structures (e.g., channel and/or ridge) along withother circuit features, such as couplers and non-linear phase shifters.The two-step hardmask method enables a stable etch base withinsemiconductor processing environments, such as the CMOS fabricationenvironment and other suitable fabrication environments. The process istwo-step in that there is deposition of a two-layer hardmask, followedby a first photolithographic pattern, followed by a first silicon etch,then a second photolithographic pattern, and then a second silicon etch.The process can be used, for example, to form a waveguide structurehaving both ridge and channel configurations, all achieved using thesame hardmask. The second photolithographic pattern allows for theformation of the lower electrical contacts to the waveguides without acomplicated rework of the hardmask (e.g., the hardmask serves as thewaveguide mask through multiple etches, preserving structure of thewaveguide). In more detail and in accordance with one embodiment, thetwo-step process includes deposition of a two-layer hardmask of oxideand nitride over a silicon-on-insulator (SOI) or deposited guide, andthen etching the active area and waveguide pattern into the hardmask. Asis known, an “active area” is a semiconductor term which defines theareas where electronic components (e.g., gate-level components andtunable couplers, input couplers, phase shifters, etc) will be located.This standard layer is combined into the waveguide layer, and bothlayers are processed as one in an efficient manner that avoids etchingnon-uniformities associated with conventional techniques. This firstetch is a partial etch and leaves a prescribed amount of silicon left ontop of the bottom oxide, so that remaining silicon can be used for aslab region of modulators or other desired components such as salicideheater structures. The hardmask remains on top of the channel waveguidestructure, and acts as an etch mask again during the waveguide ridgemask etch. The waveguide ridge mask etch is effectively the second etchin the two-step hardmask waveguide process. In more detail, this secondetch is used to define the edges of the ridge waveguide slabs (or otherpurposeful slab), and completes the partial etch (first etch step) ofthe thinned silicon down to the bottom oxide, thereby forming a finishedchannel waveguide. The exposed thinned slab areas are then ready forselective implants for the modulators prior to the oxide deposition of ashallow trench isolation (STI) fill and polish. STI is a standard CMOSprocess step, and is optional depending on the given application. Inaddition to its ability to maintain a stable etch base, the two-layerhardmask may serve other purposes. For instance, in some embodiments thehardmask operates to control the penetration depth and configuration ofion implants used to form optical modulators and make contact to opticaldetectors. It also allows for efficient formation of complex structuresincluding waveguides and other structures (such as lateral heaters inthermo-optic circuits, as described in the previously incorporated U.S.application Ser. No. ______ (Attorney Docket 20070094)). The hardmaskalso allows integration within a chemical mechanical polishing (CMP)based process. In more detail, and in accordance with one particularembodiment, a top silicon nitride layer acts as the hardmask and as apolish stop layer for CMP, thereby preserving waveguide qualities notonly across the wafer, but from wafer to wafer. After CMP, the nitridelayer can be removed, for example, using a phosphoric acid based etchthat is selective to bottom hardmask layer of oxide. Removing thenitride allows for recovery of the original perfect waveguide, andcontinuation with CMOS based fabrication processes. The two-layerhardmask two-step etch technology also enables a number of electroniccomponents (e.g., CMOS or other) having improved operation

Nonlinear Phase Shifter

FIG. 2 illustrates a nonlinear phase shifter configured in accordancewith an embodiment of the present invention. The previous discussionwith reference to FIG. 1 is equally applicable here.

As can be seen, the nonlinear phase shifter of this example embodimentis implemented with N individually tunable rings and a number of lateralsalicide heater structures and tunable couplers. The heat generated bythe heater structures causes the optical signal within the tunable ringsto phase shift in accordance with the thermo-optic effect. In addition,the tunable couplers within the nonlinear phase shifter provide tunablecoupling between the rings and waveguide. The tunable rings can beimplemented, for example, as a tunable array of resonant elementsfabricated in silicon along with the waveguide structure. In one exampleembodiment, the tunable rings are implemented as HIC silicon opticalwaveguides, and the salicide heater structures are implemented asdescribed in the previously incorporated U.S. application Ser. No.______ (Attorney Docket 20070094).

In more detail, the salicide heaters allow for greater control overresistivity and uniformity, such that the heaters can operate at CMOSvoltage levels (e.g., 0-3.3 volts). In addition, the salicide heatersallow larger temperature fluctuations. Moreover, the salicide heaters donot require shared physical modifications to the waveguide. Nor do thesalicide heaters employ any ion implantation. Rather, the heaters arefree-standing salicide structures, which can be formed using acombination of CMOS and photonic processing steps. In this sense, thelateral salicide heater structures are distinct from the waveguidestructure (i.e., the heaters are not embedded in the cladding or corematerials making up the waveguide, or otherwise in physical contact withthe waveguide). The free-standing salicide heaters allow the index ofrefraction variation to be preserved (i.e., uniformity of the refractiveindex for the cladding all the way around the waveguide). In accordancewith one particular embodiment, the salicide heaters are formed usingcobalt as the transitional thin film metal, thereby providing cobaltsalicide (CoSi₂) structures that are the result of a combination of CMOSand photonic processing steps. The salicide heaters allow efficientcoupling of thermal energy by allowing closer placement of the heatersto waveguide, thereby keeping the waveguide below the modal field. Thisalso enables lower power operation and higher speed operation, as thesalicide heaters do not require as great a thermal load to dissipateinto bulk dielectric. The heater thickness can vary as needed, dependingon factors such as power and duration and/or frequency of heatingcycles, but in one particular embodiment ranges from about 80 Angstromsto 1000 Angstroms. Note, however, that any suitable thicknesses can beused up to the full thickness of the waveguide. The salicide heaters canbe shaped or otherwise run proximate the waveguide and/or tunable ringsat a distance, for instance, within 0.5 microns, without impeding theeffective index variation. The heater structures can be configured withmetal contacts that allow power to be applied to each salicide heater,which in turn generates heat for inducing the desired thermo-opticeffect (e.g., purposeful adjustment to effective phase delay andcoupling coefficient). In the application depicted in FIG. 2, apercentage of radiation (anywhere from 0.001% to 99.99%) traveling inthe waveguide is coupled into the rings by the tunable couplers,depending on power applied to the salicide heaters in each tunablecoupler and the desired coupling factor. The radiation traveling in thewaveguide and rings is phase shifted by the localized heat from thesalicide heater structures, and in accordance with the thermo-opticeffect. Numerous schemes can be used to apply power to the heaterstructures to obtain the desired waveguide phase response (e.g., rangingfrom simple heater power switching schemes to feedback with sensing andmonitoring schemes that use real-time adjustments to the applied heaterpower to get the desired phase response out of the waveguide). Thepresent invention is not intended to be limited to any such scheme. Notethat the salicide structure may be shaped differently to suit the givenapplication, as opposed to having the elongated heater elements. Forinstance, the salicide structure may be shaped as a square orrectangular block or land or other suitable shape that runs proximatethe waveguide and/or rings. Alternatively, the heating element mayinclude a number of elongated and/or short runs that meander in variousdirections proximate a similarly meandering waveguide structure. Heatercontact pads can be provided for each heating element, to allow a biasto be applied to activate heating. In short, the salicide structure canbe shaped to suit a specific application. In addition, any number ofcontact configurations can be used, so long as long as power can bedelivered to each heater element. Example metals suitable for use informing the contacts include gold, cobalt, tungsten, nickel, titanium,and platinum. In one particular embodiment, the heater structures aremade with cobalt and the contacts (and any vias) are made with tungsten.

Optical Latch

FIG. 3 illustrates an optical latch employing external optical sourcesCW1 and CW2, in accordance with an embodiment of the present invention.

As can be seen, the latch in this example embodiment is implemented withtwo nonlinear interferometer optical comparators as discussed withreference to FIGS. 1 and 2. In addition, the optical comparators formingthe latch are resonantly enhanced, in that the optical latch employs aring-in-a-ring configuration. For each comparator, the inner ring isshown outside the outer ring for purposes of better illustration, but isactually inside the outer ring when deployed. In particular, by placingeach of the nonlinear phase shifters within a second resonatorstructure, the nonlinear phase shift can be enhanced by two to threeorders of magnitude, thereby dramatically lowering the switching power,and increasing the A/D dynamic range.

In addition, a tunable coupler (TC2-D) is provided on the left opticalcomparator (OC2) that allows reset pulse OC2 bias to be applied, and atunable coupler (TC1-D) is provided on the right optical comparator(OC1) that allows set pulse OC1 bias to be applied. Each of the innerrings of OC1 and OC2 is coupled to its outer ring by a tunable coupler(TC1-B and TC2-B, respectively) as well. Likewise, each of OC1 and OC2includes a tunable coupler (TC1-C and TC2-C, respectively) that providesa corresponding output: Out 1 (Q) for OC1 and Out 2 (not-Q) for OC2.

This optical latch is triggered on by a set pulse at the set pulse OC1bias input. Subsequently, it can be triggered off by a reset pulse atthe reset pulse OC2 bias input. Such a set/reset scheme allows theoutput from a optical bus to be brought into a cell (optical latch)without slowing it down with electronic switching. By adding a secondlatch, the gating of information to the bus can be controlled at a muchgreater rate of operation than could be achieved with an electroniccomponent alone. A similar configuration allows for storing and rapidlygating information to an optical bus. In this example configuration theelectronic component writes a state to the latch. Once the bus comesactive, the information is rapidly clocked into the optical bus throughthe second latch. Simpler output architecture can be achieved by runningthe output of the latch through an optically addressed bus switch. Thiscan be further extended by combining latches to achieve a serial toparallel converter to rapidly burst in data serially at each wavelength.Other such applications will be apparent in light of this disclosure.

The internal ring of each optical comparator represents a very lowthreshold, multiple-level shifting optical comparator, where the Resetand Set pulses of each comparator provide a multiple input controlintensity. The added internal optically resonant loop, in essencemultiplies the nonlinearity of the nonlinear optical loop mirror by thefinesse of the optical cavity. This effect is beneficial, for example,for very low thresholds in high-bit photonic A/D conversion. The tunablecouplers TC1-B and TC2-B can be tuned to provide a percentage (e.g.,anywhere from 0.001% to 99.99%) of signal in the outer ring to the innerring in both clockwise and counter-clockwise directions.

In operation, each optical comparator OC1 and OC2 acts as follows. Theinput pulse (CW1 or CW2) is split by a tunable coupler (TC1-A or TC2-A),wherein a portion (determined by the couplers coupling factor k) of theinput pulse follows a clockwise path around the waveguide loop, and theremainder follows a counter-clockwise path around the waveguide loop.Because of phase shifts across this tunable coupler (TC1-A or TC2-A)both into and out of the loop, these pulses interfere and normallycancel on the output and add at the input. Therefore the net effect isreflection of the input pulse from the optical comparator (light travelsout the path it originally came in on). This cancellation is assured ina Sagnac interferometer as the pulses transit identical paths and thusobtain equal phase shifts. By making the tunable coupler (TC1-A orTC2-A) unbalanced (e.g., tuning the coupler to 70:30 instead of 50:50),the pulses in each direction have unequal intensities. The nonlinearphase shifter then produces unequal phase shifts due to the unequalintensities. They then do not destructively interfere at the output, andthe input pulse switches, or couples, to the output path. As previouslyexplained, this intensity-dependent optical switching (or comparison) isbased upon Self Phase Modulation (SPM). Should a different wavelengthpulse or different same wavelength source enter the control arm (Resetand Set pulses enter via TC1-D and TC2-D), the nonlinear phase shift iscaused by Cross Phase Modulation (XPM). With the added loop and tunablecoupler (TC1-B or TC2-B) the finesse of the cavity containing the phasemodifying element can be optimized allowing a reduction in the powerneeded to achieve the phase shift of ˜1/cavity finesse.

In one embodiment, the control pulse (Reset and Set pulses enter viaTC1-D and TC2-D) enters the loop in just one direction, it allows thecoupler to be returned to 50:50 coupling, and the loop will switchbetween 0 and 100% of the input (CW1 or CW2) when the sum of that inputplus the control intensity Reset or Set pulse) exceeds the loopthreshold (differential phase shift of pi radians). This provides asettable/changeable threshold for the optical comparator. Note, however,that the optionally tunable couplers TC1-D and TC2-D can be tuned toprovide a percentage (e.g., anywhere from 0.001% to 99.99%) of controlpulse in the both clockwise and counter-clockwise directions.

In alternative embodiments, an optical latch can be implemented with asingle loop body with the nonlinear interferometer optical comparatorsshown in FIGS. 1 and 2 (i.e., no ring-in-a-ring configuration), wherethe inner ring is eliminated and the nonlinear phase shifter is moved tothe outer ring where the inner ring tunable coupler (TC1-B and TC2-B) isshown. As will be appreciated, that tunable coupler (TC1-B and TC2-B) isnot needed for a single ring configuration.

In either the ring-in-ring or single ring configurations, the outputs ofeach optical comparator (Out 1 for OC1 and Out 2 for OC2) providecomplementary signals Q and not-Q, where a percentage (e.g., about 30%to 50%, depending on the coupling factor the output couplers TC1-C andTC2-C) of output signal can be coupled to the other comparator.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

1. An integrated optical circuit device, comprising: a first integratedwaveguide loop for guiding optical signals; a nonlinear phase shiftingelement for phase shifting signals in the first integrated waveguideloop, wherein the nonlinear phase shifting element includes one or moretunable couplers configured with salicide heating elements for opticallycoupling resonant elements to the first integrated waveguide loop; atunable coupler for providing an input pulse in both clockwise andcounter-clockwise direction of the first integrated waveguide loop; andan input coupler for providing a control pulse in at least one directionof the first integrated waveguide loop.
 2. The device of claim 1 whereinthe first integrated waveguide loop is a high index contrast (HIC)silicon waveguide.
 3. An integrated optical circuit device, comprising:a first integrated waveguide loop for guiding optical signals; anonlinear phase shifting element for phase shifting signals in the firstintegrated waveguide loop, wherein the nonlinear phase shifting elementincludes n individually tunable resonant elements and a salicide heaterstructure for providing heat to the n individually tunable resonantelements. a tunable coupler for providing an input pulse in bothclockwise and counter-clockwise direction of the first integrated waveguide loop; and an input coupler for providing a control pulse in atleast one direction of the first integrated wave guide loop.
 4. Thedevice of claim 3 further comprising: a second integrated waveguide loopfor guiding optical signals: a nonlinear phase shifting element forphase shifting signals in the second integrated waveguide loop; atunable coupler for providing an input pulse in both clockwise andcounter-clockwise direction of the second integrated waveguide loop; andan input coupler for providing a control pulse in at least one directionof the second integrated wave guide loop.
 5. The device of claim 3wherein the first integrated waveguide loop is configured with an innerring and an outer ring optically coupled to the inner ring, and thenonlinear phase shifting element is in the inner ring.
 6. The device ofclaim 1 further wherein the first integrated waveguide loop isconfigured with an inner ring and an outer ring optically coupled to theinner ring, and the nonlinear phase shifting element is in the innerring.
 7. The device of claim 1 further comprising: a second integratedwaveguide loop for guiding optical signals; a nonlinear phase shiftingelement for phase shifting signals in the second integrated waveguideloop; a tunable coupler for providing an input pulse in both clockwiseand counter-clockwise direction of the second integrated waveguide loop;and an input coupler for providing a control pulse in at least onedirection of the second integrated waveguide loop.
 8. The device ofclaim 7 wherein the second integrated waveguide loop is a high indexcontrast (HIC) silicon waveguide.
 9. The device of claim 7 whereinnonlinear phase shifting element for phase shifting signals in thesecond integrated waveguide loop includes n individually tunableresonant elements.
 10. The device of claim 9 wherein the nonlinear phaseshifting element for phase shifting signals in the second integratedwaveguide loop includes a salicide heater structure for providing heatto the n individually tunable resonant elements.
 11. The device of claim7 wherein the nonlinear phase shifting element for phase shiftingsignals in the second integrated waveguide loop includes one or moretunable couplers configured with salicide heating elements for opticallycoupling resonant elements to the second integrated waveguide loop. 12.The device of claim 7 further wherein the second integrated waveguideloop is configured with an inner ring and an outer ring opticallycoupled to the inner ring, and nonlinear phase shifting element forphase shifting signals in the second integrated waveguide loop is in theinner ring.
 13. An integrated optical circuit device, comprising: afirst a nonlinear interferometer optical comparator comprising: a firstintegrated waveguide loop for guiding optical signals; a nonlinear phaseshifting element for phase shifting signals in the first integratedwaveguide loop; a tunable coupler for providing an input pulse in bothclockwise and counter-clockwise direction of the first integratedwaveguide loop; and an input coupler for providing a control pulse in atleast one direction of the first integrated waveguide loop; a second anonlinear interferometer optical comparator operatively coupled to thefirst nonlinear interferometer optical comparator, comprising: a secondintegrated waveguide loop for guiding optical signals; a nonlinear phaseshifting element for phase shifting signals in the second integratedwaveguide loop; a tunable coupler for providing an input pulse in bothclockwise and counter-clockwise direction of the second integratedwaveguide loop; and an input coupler for providing a control pulse in atleast one direction of the second integrated waveguide loop; whereineach of the nonlinear phase shifting elements includes one or moresalicide heater structures.
 14. The device of claim 13 wherein each ofthe first and second integrated waveguide loops is a high index contrast(HIC) silicon waveguide.
 15. The device of claim 13 wherein each of thenonlinear phase shifting elements includes n individually tunableresonant elements.
 16. The device of claim 13 wherein each of thenonlinear phase shifting elements includes a plurality of salicideheater structures.
 17. The device of claim 13 further wherein each ofthe first and second integrated waveguide loops is configured with aninner ring and an outer ring optically coupled to the inner ring, andeach of the nonlinear phase shifting elements is in the inner ring. 18.An integrated optical circuit device, comprising: a first a nonlinearinterferometer optical comparator comprising: a first integratedwaveguide loop for guiding optical signals; a nonlinear phase shiftingelement for phase shifting signals in the first integrated waveguideloop; a tunable coupler for providing an input pulse in both clockwiseand counter-clockwise direction of the first integrated waveguide loop;and an input coupler for providing a control pulse in at least onedirection of the first integrated waveguide loop; a second a nonlinearinterferometer optical comparator operatively coupled to the firstnonlinear interferometer optical comparator, comprising: a secondintegrated waveguide loop for guiding optical signals; a nonlinear phaseshifting element for phase shifting signals in the second integratedwaveguide loop; a tunable coupler for providing an input pulse in bothclockwise and counter-clockwise direction of the second integratedwaveguide loop; and an input coupler for providing a control pulse in atleast one direction of the second integrated waveguide loop; whereineach of the first and second integrated waveguide loops is a high indexcontrast (HIC) silicon waveguide, and each of the nonlinear phaseshifting elements includes n individually tunable resonant elements andone or more salicide heater structures.
 19. The device of claim 18wherein each of the nonlinear phase shifting elements includes aplurality of salicide heater structures.
 20. The device of claim 18further wherein each of the first and second integrated waveguide loopsis configured with an inner ring and an outer ring optically coupled tothe inner ring, and each of the nonlinear phase shifting elements is inthe inner ring.